AB1678 CONSTRUCTION OF A COMPOSITE SCORE FOR PATIENT SELF-REPORT OF FLARE IN OSTEOARTHRITIS: A COMPARISON OF METHODS WITH THE FLARE-OA-16 QUESTIONNAIRE
Authors: F. Queiroga, J. Epstein, M.L. Erpelding, L. King, M. Soudant, E. Spitz, J.F. Maillefert, B. Fautrel, L. Callahan, L. March, D. Hunter, F. Guillemin
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Having a score to assess the occurrence and severity of flares of knee or hip osteoarthritis (OA) to guide interventions is essential. <h3>Objectives</h3> To compare different methods of constructing a composite score for the Flare-OA-16 self-reported questionnaire for measuring knee and hip OA flare, defined as a cluster of symptoms of sufficient duration and intensity to require initiation, change or increase in therapy [1]. <h3>Methods</h3> Participants with a physician diagnosis of knee and hip OA completed a validated 16-item questionnaire [2,3] assessing five dimensions of flare in OA: pain, swelling, stiffness, psychological aspects, and consequences of symptoms, endorsed by OMERACT. Three estimation methods were compared: the score obtained i) by second-order confirmatory factor analysis (CFA) weighting the factor loadings in a linear combination of the five dimensions; ii) by logistic regression, modeling the probability of having a flare according to the participant's self-report (yes/no); and iii) by Rasch method, using the average of the weighted scores from a Rasch model in each dimension. For the scores obtained by the three methods, the disordered items were modified, and then the scores were standardized on a scale from 0 to 10. The distribution (floor effect without flare (FF) and ceiling effect with flare (CF)) of the scores in each model was compared. The similarity between the scores was analyzed by intraclass correlation coefficient (ICC) and their performance were compared by areas under the ROC curves (AUC) and 95% confidence interval. The intra-score test-retest reliability at 15 days was assessed by ICC. <h3>Results</h3> In a sample of 381 participants with complete questionnaires, 247 reported having a flare. With CFA, good fit indices (CFI=0.94; RMSEA=.08) justified the estimation of an overall score mean=3.90 (SD=2.79), with FF effect 27.6% and CF 2.0%. For the logistic regression estimation, the overall score was mean=6.48 (SD=3.13), with FF 0% and CF 34.0% effect. With the Rasch model, the composite score was mean=4.15 (SD=2.45), with FF 18.7% and CF 0% effect. Similarity analysis indicated a greater concordance between the CFA and Rasch scores (ICC=.99) than between the logistic regression score and the two others (ICC=.87 for each). The ROC curve indicated similar performance of the overall scores estimated by logistic model (AUC=.88 [.85-.92]), by CFA (AUC=.86 [.82-.90]) and by Rasch model (AUC=.86 [.82-.90]). The performance in terms of reproducibility was ICC=.84[.95-.90] for Rasch and CFA scores and ICC=.78[.66-86] for logistic model. <h3>Conclusion</h3> This comparison of methods for constructing a global score for knee and hip OA flare explored three satisfactory alternatives. The second-order CFA confirmed the uniqueness of the flare construct measure, the logistic model had a slight superiority explained by the anchor variable used (patient-reported flare), and the Rasch model ensured that an interval scale was obtained for each dimension. The distribution of scores with the lowest combination of floor and ceiling effects was in favor of the Rasch model. The next step will be to document their respective performance in terms of sensitivity to change. A score obtained from the patient's point of view can help increase the adherence to the prescribed treatment and help physicians to optimize the scheduling and delivery of medical consultation. <h3>References</h3> [1]Guillemin F., et al. Developing a Preliminary Definition and Domains of Flare in Knee and Hip Osteoarthritis (OA): Consensus Building of the Flare-in-OA OMERACT Group. J Rheumatol. 2019 Sep;46(9):1188–91. [2]Traore Y., et al. Development and validation of the Flare-OA questionnaire for measuring flare in knee and hip osteoarthritis. Osteoarthritis Cartilage. 2022 May;30(5):689–96. [3]Queiroga F., et al. Validation et réduction d'une échelle de mesure des poussées dans l'arthrose de la hanche et du genou par un modèle de Rasch. Rev Épidémiol Santé Publique. 2022 May;70:S70. <h3>Acknowledgements</h3> We acknowledge the participants of the study samples that were used in the study, without whom this research could not been possible. <h3>Financial support</h3> This work was supported partly by the French PIA project "Lorraine Université d'Excellence", reference ANR-15-IDEX-04-LUE. <h3>Disclosure of Interests</h3> None Declared.